Research Article
Lattice Dynamics and Transport Properties
of Multiferroic DyMn
2
O
5
Javed Ahmad,
1
Syed Hamad Bukhari,
1
M. Tufiq Jamil,
1
Mehr Khalid Rehmani,
1
Hammad Ahmad,
2
and Tahir Sultan
3
1
Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistan
2
Nanoscience and Technology Department, National Center for Physics, Quaid-i-Azam University Campus, Islamabad 45320, Pakistan
3
Department of Civil Engineering, Bahauddin Zakariya University, Multan 60800, Pakistan
Correspondence should be addressed to Javed Ahmad; dr.j.ahmad@gmail.com
Received 12 December 2016; Revised 16 February 2017; Accepted 20 February 2017; Published 7 March 2017
Academic Editor: Mohindar S. Seehra
Copyright © 2017 Javed Ahmad et al. Tis is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
We have investigated the optical and electrical properties of polycrystalline DyMn
2
O
5
synthesized by sol-gel method. Analysis of
the refectivity spectrum has led to the observation of 18 infrared (IR) active phonon modes out of 36 predicted ones. We discuss
the results in terms of diferent phonon bands originated as a result of atomic vibrations. Moreover, the optical energy band gap of
()
∼ 1.78 eV has been estimated from optical conductivity (
1
()) spectrum. Te energy band gap and optical transitions were
also determined from UV-visible absorption spectrum and band gap of
(UV)
∼ 1.57 eV was estimated. Moreover, DC electrical
resistivity shows the p-type polaronic conduction above room temperature.
1. Introduction
Manganites Mn
2
O
5
, typical type-II multiferroics, usually
show large coupling between spin (magnetism), charge (fer-
roelectricity), and lattice (structure). Mn
2
O
5
compounds
show cascade of phase transitions with characteristic temper-
ature at N´ eel transition
= 40–45 K and ferroelectric tran-
sition at
= 28–39 K and ordering of rare-earth moments
occurs below 10K [1]. Until recently, it is well known that
Mn
2
O
5
crystallize in the orthorhombic structure with Pbam
space group at room temperature [2]. However, very recently
it is proposed that Mn
2
O
5
crystallize in two possible mon-
oclinic space groups and 2 depending on the existence
of polarization in plane and along axis, respectively [3].
Among the family of Mn
2
O
5
, DyMn
2
O
5
exhibits
remarkable magnetodielectric behavior as compared to other
Mn
2
O
5
compounds [4]. An unconventional behavior of
phonon anomalies in Mn
2
O
5
( = Bi, Eu, Dy) has been
observed in the paramagnetic phase [5]. Tey have suggested
that these anomalies at new characteristics temperature
∗
∼
1.5
are related to the spin-phonon coupling and signaling
a transition between states. Moreover, spin-phonon coupling
has been observed slightly above
indicating the drastic
change in phonon frequency due to magnetic feld and
temperature [6, 7]. Remarkably, recently we have observed an
unconventional magnetodielectric efect in DyMn
2
O
5
above
, where the infrared and Raman phonons have shown
spin-phonon coupling and confrm the strong correlation
between spin, charge, and lattice degree of freedom [8].
Such a strong interplay between many degrees of freedom
in the paramagnetic phase is a special characteristic of
Mn
2
O
5
family [5–9]. Te knowledge of lattice vibrations
and their correlation to diferent conduction mechanisms
is of crucial importance for engineering the materials for
various technological applications. However, currently there
is no report on the correlation between IR active phonon and
the conduction mechanism for DyMn
2
O
5
.
In this work, we have measured the IR refectivity spec-
trum of DyMn
2
O
5
and assign the IR active phonon modes
with theoretically calculated modes. In addition, we have per-
formed UV-visible spectroscopy and temperature dependent
electrical response to observe the microscopic conduction
mechanism. Te main objective of this paper is to investigate
the lattice vibration in DyMn
2
O
5
and the possible correlation
Hindawi
Advances in Condensed Matter Physics
Volume 2017, Article ID 5389573, 8 pages
https://doi.org/10.1155/2017/5389573